The present invention relates to train location systems and, more particularly, to train location systems for continuously and accurately identifying the location of a train on or within a trackway system using a train-mounted geo-positional receiver system and inertial sensors in combination with other signals provided from one or more train-mounted sensors.
Various systems have been developed to track the movement of and location of railway trains on track systems.
In its simplest form, train position can be ascertained at a central control facility by using information provided by the crew, i.e., the train crew periodically radios the train position to the central control facility; this technique diverts the attention of the crew while reporting the train position, often requires several xe2x80x9cretriesxe2x80x9d where the radio link is intermittent, and the position information rapidly ages.
Early efforts have involved trackside equipment to provide an indication of the location of a train in a trackway system. Wayside devices can include, for example, various types of electrical circuit completion switches/systems by which an electrical circuit is completed in response to the passage of a train. Since circuit completion switches/system are typically separated by several miles, this technique provides a relatively coarse, discrete resolution that is generally updated or necessarily supplemented by voice reports by the crew over the radio link.
In addition, information from one or more wheel tachometers or odometers can be used in combination with timing information to provide distance traveled from a known start or waypoint position. Since tachometer output can be quite xe2x80x9cnoisyxe2x80x9d from a signal processing standpoint and accuracy is a function of the presence or absence of wheel slip, the accuracy of the wheel-based distanced-traveled information can vary and is often sub-optimal.
Other and more sophisticated trackside arrangements include xe2x80x9cbeaconsxe2x80x9d that transmit radio frequency signals to a train-mounted receiver that can triangulate among several beacons to determine location.
While trackside beacon systems have historically functioned in accordance with their intended purpose, trackside systems can be expensive to install and maintain. Trackside systems tend not to be used on a continent-wide or nation-wide basis, leaving areas of the track system without position-locating functionality (viz., xe2x80x9cdarkxe2x80x9d territory).
More recently, global navigation satellite systems such as the Global Positioning System (GPS) and the nationwide Differential GPS (NDGPS), have been used to provide location information for various types of moving vehicles, including trains, cargo trucks, and passenger vehicles. GPS and similar systems use timed signals from a plurality of orbital satellites to provide position information, and, additionally, provide accurate time information. The time information can include a highly accurate 1PPS (1-pulse-per-second) output that can be used, for example, to synchronize (or re-synchronize) equipment used in conjunction with the GPS receiver. The GPS/DGPS receivers require a certain amount of time to acquire the available satellite signals to calculate a positional fix. While the GPS system can be used to provide position information, GPS receivers do not function in tunnels, often do not function well where tracks are laid in steep valleys, and can fail to operate or operate intermittently in areas with substantial electromagnetic interference (EMI) and radio frequency interference (RFI). When a GPS system is operated on a fast-moving vehicle, the location information becomes quickly outdated. In addition, the accuracy of the GPS system for non-military applications is such that track occupancy (which track a train is on among two or more closely spaced tracks) cannot be determined consistently and reliably.
Current philosophy in train systems is directed toward higher speed trains and optimum track utilization. Such train systems require ever more resolution in train location and near real-time or real time position, distance from a known reference point, speed, and direction information. In addition to locating a train traveling along a particular trackway to a resolution of one or two meters, any train location system should be able to locate a train along one of several closely spaced, parallel tracks. Since track-to-track spacing can be as little as three meters, any train location system must be able to account for train location on any one of a plurality of adjacent trackways or determine track occupancy at a turnout or other branch point.
In view of the above, it is an object of the present invention, among others, to provide a train location system and method that utilizes geo-reconciliation to improve system performance.
It is another object of the present invention to provide a train location system and method that solve the track occupancy problem when a train passes through a turnout onto one of two or more tracks leading from the turnout.
The present invention provides a train location system that utilizes inertially sensed orthogonal acceleration inputs and turn-rate information combined with other inputs, such as those provided by one or more wheel-mounted tachometers and pre-stored or downloaded-on-the-fly track signature profiles, to provide information inputs related to velocity and location. In addition, GPS/DGPS information is used to provide processed outputs indicative of position and related variables.
The present invention blends a plurality of navigation solutions (i.e., three) together to provide the desired information outputs. The three solutions possess complimentary error characteristics and are used in conjunction with exogenous data in an optimal estimator designed (i.e., tuned) specifically for rail applications and subjected to motion constraints reflecting the physical motion limitations of a locomotive. The complimentary nature of the error mechanisms involved enables the desired variables, viz., position, speed, etc., to be uniquely observed mathematically and thence computed.
The present invention incorporates the concept of geo-reconciliation by which information vectors from sources having different error characteristics are geo-reconciled to reduce the adverse affect of short- and long-term errors. In the context of the velocity vector, for example, an inertially derived velocity vector is geo-reconciled with a geo-computed velocity vector obtained, for example, from the calibrated wheel tachometer and the train forward axis or track centerline axis. In general, the inertially obtained and the tachometer derived velocity vectors will be different based upon the cumulative errors in each system. An optimal estimator functions to blend two such values to obtain the geo-reconciled velocity vector. With each successive computation sequence, the optimal estimator functions to estimate the error mechanisms and effect corrections to successively propagate position and the associated uncertainty along the track.
Fault detection logic is used to correctly maintain track occupancy at branch points. A solution is computed along each of the two diverging tracks when passing through a turnout. Forcing the solution to propagate along the would-be incorrect track subsequently shapes estimated error states in a distinguishable manner and does so with adequate diversity to make the track occupancy decision with sufficient confidence.
An optimal estimator, preferably in the form of a Kalman filter, extended Kalman filter or variants thereof, is provided with state equations that define estimated position in response to the various information inputs, measurements, and signals. The use of an optimal estimator allows continuous high-veracity position information outputs, including position information outputs under conditions in which the input information is noisy, momentarily interrupted, and/or otherwise sub-optimal.
Additionally, the present invention drives the average lateral and vertical velocity to null and the cross-track velocity to null as an effective way of enforcing the physical constraints of locomotion.
Position information from a plurality of trains can be provided to a central track control or command center to allow more efficient utilization of the train/track system.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description to follow, taken in conjunction with the accompanying drawings, in which like parts are designated by like reference characters.